Peacekeepers monitor and observe peace processes in post-conflict areas and assist ex-combatants in implementing the peace agreements they may have signed. Such assistance comes in many forms, including confidence-building measures, power-sharing arrangements, electoral support, strengthening the rule of law, and economic and social development. Accordingly, UN peacekeepers (often referred to as Blue Berets or Blue Helmets because of their light blue berets or helmets) can include soldiers, police officers, and civilian personnel.

Most of these operations are established and implemented by the United Nations itself, with troops serving under UN operational control. In these cases, peacekeepers remain members of their respective armed forces, and do not constitute an independent "UN army," as the UN does not have such a force. In cases where direct UN involvement is not considered appropriate or feasible, the Council authorizes regional organizations such as the North Atlantic Treaty Organization (NATO),[4] the Economic Community of West African States, or coalitions of willing countries to undertake peacekeeping or peace-enforcement tasks.

Peacekeeping forces are contributed by member states on a voluntary basis. As of 31 December 2013, the total size of the peacekeeping force is 98,200 police, troops, and military experts. European nations contribute nearly 6,000 units to this total. Pakistan, India, and Bangladesh are among the largest individual contributors with around 8,000 units each. African nations contributed nearly half the total, almost 44,000 units.[6]

Once a peace treaty has been negotiated, the parties involved might ask the United Nations for a peacekeeping force to oversee various elements of the agreed upon plan. This is often done because a group controlled by the United Nations is less likely to follow the interests of any one party, since it itself is controlled by many groups, namely the 15-member Security Council and the intentionally diverse United Nations Secretariat.

If the Security Council approves the creation of a mission, then the Department of Peacekeeping Operations begins planning for the necessary elements. At this point, the senior leadership team is selected. The department will then seek contributions from member nations. Since the UN has no standing force or supplies, it must form ad hoc coalitions for every task undertaken. Doing so results in both the possibility of failure to form a suitable force, and a general slowdown in procurement once the operation is in the field. Romeo Dallaire, force commander in Rwanda during the Rwandan Genocide there, described the problems this poses by comparison to more traditional military deployments:

He told me the UN was a "pull" system, not a "push" system like I had been used to with NATO, because the UN had absolutely no pool of resources to draw on. You had to make a request for everything you needed, and then you had to wait while that request was analyzed... For instance, soldiers everywhere have to eat and drink. In a push system, food and water for the number of soldiers deployed is automatically supplied. In a pull system, you have to ask for those rations, and no common sense seems to ever apply.

While the peacekeeping force is being assembled, a variety of diplomatic activities are being undertaken by UN staff. The exact size and strength of the force must be agreed to by the government of the nation whose territory the conflict is on. The Rules of Engagement must be developed and approved by both the parties involved and the Security Council. These give the specific mandate and scope of the mission (e.g. when may the peacekeepers, if armed, use force, and where may they go within the host nation). Often, it will be mandated that peacekeepers have host government minders with them whenever they leave their base. This complexity has caused problems in the field.

When all agreements are in place, the required personnel are assembled, and final approval has been given by the Security Council, the peacekeepers are deployed to the region in question.

In 1993, annual UN peacekeeping costs had peaked at some $3.6 billion, reflecting the expense of operations in the former Yugoslavia and Somalia. By 1998, costs had dropped to just under $1 billion. With the resurgence of larger-scale operations, costs for UN peacekeeping rose to $3 billion in 2001. In 2004, the approved budget was $2.8 billion, although the total amount was higher than that. For the fiscal year which ended on June 30, 2006, UN peacekeeping costs were about US$5.03 billion.

Member states owed approximately $1.20 billion in current and back peacekeeping dues as of June 2004.

A United Nations peacekeeping mission has three power centers. The first is the Special Representative of the Secretary-General, the official leader of the mission. This person is responsible for all political and diplomatic activity, overseeing relations with both the parties to the peace treaty and the UN member-states in general. They are often a senior member of the Secretariat. The second is the Force Commander, who is responsible for the military forces deployed. They are a senior officer of their nation's armed services, and are often from the nation committing the highest number of troops to the project. Finally, the Chief Administrative Officer oversees supplies and logistics, and coordinates the procurement of any supplies needed.

United Nations peacekeeping was initially developed during the Cold War as a means of resolving conflicts between states by deploying unarmed or lightly armed military personnel from a number of countries, under UN command, to areas where warring parties were in need of a neutral party to observe the peace process. Peacekeepers could be called in when the major international powers (the five permanent members of the Security Council) tasked the UN with bringing closure to conflicts threatening regional stability and international peace and security. These included a number of so-called "proxy wars" waged by client states of the superpowers. As of February 2009, there have been 63 UN peacekeeping operations since 1948, with sixteen operations ongoing. Suggestions for new missions arise every year.

Returning its attention to the conflict between Israel and its Arab neighbors, the United Nations responded to Suez Crisis of 1956, a war between the alliance of the United Kingdom, France, and Israel, and Egypt, which was supported by other Arab nations. When a ceasefire was declared in 1957, CanadianSecretary of State for External Affairs[7] (and future Prime Minister) Lester Bowles Pearson suggested that the United Nations station a peacekeeping force in the Suez in order to ensure that the ceasefire was honored by both sides. Pearson had initially suggested that the force consist of mainly Canadian soldiers, but the Egyptians were suspicious of having a Commonwealth nation defend them against the United Kingdom and her allies. In the end, a wide variety of national forces were drawn upon to ensure national diversity. Pearson would win the Nobel Peace Prize for this work, and he is today considered a father of modern peacekeeping.[citation needed]

In 1988, the Nobel Peace Prize was awarded to the United Nations peacekeeping forces. The press release stated that the forces "represent the manifest will of the community of nations" and have "made a decisive contribution" to the resolution of conflict around the world.

The end of the Cold War precipitated a dramatic shift in UN and multilateral peacekeeping. In a new spirit of cooperation, the Security Council established larger and more complex UN peacekeeping missions, often to help implement comprehensive peace agreements between belligerents in intra-State conflicts and civil wars. Furthermore, peacekeeping came to involve more and more non-military elements that ensured the proper functioning of civic functions, such as elections. The UN Department of Peacekeeping Operations was created in 1992 to support this increased demand for such missions.

By and large, the new operations were successful. In El Salvador and Mozambique, for example, peacekeeping provided ways to achieve self-sustaining peace. Some efforts failed, perhaps as the result of an overly optimistic assessment of what UN peacekeeping could accomplish. While complex missions in Cambodia and Mozambique were ongoing, the Security Council dispatched peacekeepers to conflict zones like Somalia, where neither ceasefires nor the consent of all the parties in conflict had been secured. These operations did not have the manpower, nor were they supported by the required political will, to implement their mandates. The failures—most notably the 1994 Rwandan Genocide and the 1995 massacre in Srebrenica and Bosnia and Herzegovina—led to a period of retrenchment and self-examination in UN peacekeeping.

That period led, in part, to the United Nations Peacebuilding Commission, which works to implement stable peace through some of the same civic functions that peacekeepers also work on, such as elections. The Commission currently works with six countries, all in Africa.[8]

The UN Charter stipulates that to assist in maintaining peace and security around the world, all member states of the UN should make available to the Security Council necessary armed forces and facilities. Since 1948, close to 130 nations have contributed military and civilian police personnel to peace operations. While detailed records of all personnel who have served in peacekeeping missions since 1948 are not available, it is estimated that up to one million soldiers, police officers and civilians have served under the UN flag in the last 56 years. As of June 2013, 114 countries were contributing a total 91,216 military observers, police, and troops to United Nations Peacekeeping Operations.

As of 29 February 2016, 124 countries were contributing a total of 105,314 personnel in Peacekeeping Operations, with Ethiopia leading the tally (8,324), followed by India (7,695) and Bangladesh (7,525).[9]

As of 28 February 2015, 120 countries were contributing a total of 104,928 personnel in Peacekeeping Operations, with Bangladesh leading the tally (9446).[11]

The former head of the Department of Peacekeeping Operations, Jean-Marie Guéhenno, had reminded Member States that "the provision of well-equipped, well-trained and disciplined military and police personnel to UN peacekeeping operations is a collective responsibility of Member States. Countries from the South should not and must not be expected to shoulder this burden alone."

As of March 2008, in addition to military and police personnel, 5,187 international civilian personnel, 2,031 UN Volunteers and 12,036 local civilian personnel worked in UN peacekeeping missions.[12]

Through April 2008, 2,468 people from over 100 countries have been killed while serving on peacekeeping missions.[13] Many of those came from India (127), Canada (114) and Ghana (113). Thirty percent of the fatalities in the first 55 years of UN peacekeeping occurred in the years 1993-1995. About 4.5% of the troops and civilian police deployed in UN peacekeeping missions come from the European Union and less than one percent from the United States (USA).[14]

The rate of reimbursement by the UN for troop-contributing countries per peacekeeper per month include: $1,028 for pay and allowances; $303 supplementary pay for specialists; $68 for personal clothing, gear and equipment; and $5 for personal weaponry.[15]

According to scholar Page Fortna, there is strong evidence that the presence of peacekeepers significantly reduces the risk of renewed warfare; more peacekeeping troops leads to fewer battlefield deaths; and more peacekeeping troops leads to fewer civilian deaths.[16]

The findings of one study suggests that stronger PKO mandates and a doubling of the PKO budget would reduce armed conflicts by up to two thirds relative to a scenario without PKOs.[17]

Reporters witnessed a rapid increase in prostitution in Cambodia and Mozambique after UN peacekeeping forces moved in. In the 1996 UN study "The Impact of Armed Conflict on Children", former first lady of Mozambique Graça Machel documented: "In 6 out of 12 country studies on sexual exploitation of children in situations of armed conflict prepared for the present report, the arrival of peacekeeping troops has been associated with a rapid rise in child prostitution."[18]

In response to criticism, particularly of the cases of sexual abuse by peacekeepers, the UN has taken steps toward reforming its operations. The Brahimi Report was the first of many steps to recap former peacekeeping missions, isolate flaws, and take steps to patch these mistakes to ensure the efficiency of future peacekeeping missions. The UN has vowed to continue to put these practices into effect when performing peacekeeping operations in the future. The technocratic aspects of the reform process have been continued and revitalised by the DPKO in its "Peace Operations 2010" reform agenda. This included an increase in personnel, the harmonization of the conditions of service of field and headquarters staff, the development of guidelines and standard operating procedures, and improving the partnership arrangement between the Department of Peacekeeping Operations (DPKO) and the United Nations Development Programme (UNDP), African Union and European Union. 2008 capstone doctrine entitled "United Nations Peacekeeping Operations: Principles and Guidelines"[5] incorporates and builds on the Brahimi analysis.

One suggestion to account for delays such as the one in Rwanda, is a rapid reaction force: a standing group, administered by the UN and deployed by the Security Council, that receives its troops and support from current Security Council members and is ready for quick deployment in the event of future genocides.[32]

The UN peacekeeping capacity was enhanced in 2007 by augmenting the DPKO with the new Department of Field Support (DFS). Whereas the new entity serves as a key enabler by co-ordinating the administration and logistics in UN peacekeeping operations, DPKO concentrates on policy planning and providing strategic directions.[citation needed]